For incursions specifically, it's no accident that my incursion guides speak specifically to how to tank for incursion fleets, and of my two dedicated incursion guides, one is a "How to be a Logistics in incursions" guide. ;-)
There's a good rule of thumb that it's smart to follow when you're flying in a fleet: if you have a decent number of Logis, fit for resists. If you don't, fit for buffer.
It's not a hard and fast rule. For instance, if you're flying in a fleet with Logi, you should still have enough buffer that there is time for the Logis to lock you and hold you up. And of course, even the most buffer-fit ship you have, if it's a cruiser or bigger, it should have at least some resists. There are exceptions to every rule, and situations where you want to fit for buffer even if you have a ton of Logi support. Still, it's a good rule of thumb to keep in mind. I will illustrate why. Warning: scary math follows.
If I'm sitting in my Logi, chances are pretty good that I can apply somewhere between 85 and 105 hit points of shield and/or armor to your tank, per second, per repper that I apply to you.(2) Let's average it out and say that it's 100. I generally have four reppers. Let's say I put all four on you. That's 400 raw hit points per second. But that's only 400 EHP if you have no resists at all. Most ships have resists. The more resists you have, the more effective that 400 raw hit points is going to be:
- If you have 80% resists, then that 400 raw hit points effectively becomes 2000 EHP (400 divided by 20%).
- If you have 68% resists, then that 400 raw hit points effectively becomes 1250 EHP (400 divided by 32%).
- If you have 47% resists, then that 400 raw hit points effectively becomes 750 EHP (400 divided by 53%).
This is why you'll hear Logi pilots tell you again and again, resists > buffer. You only need enough buffer to give me time to lock you after you broadcast for reps. Any buffer you have above and beyond that is wasted mid- and/or low slots, depending. I would have rather you fit another Invul instead of that LSE, another EANM instead of that plate. Again, this isn't the situation every single time. There are exceptions to every rule. But if you're in doubt, that's the factor you should keep in mind.
Back when I wrote about various ways of fitting Vagabonds, I covered this topic. A solo/quick response Vaga should have two LSEs in the mids. However, a Vaga for fleets where you expect there to be good Logi support can fit Anti-Explosive and Anti-Kinetic resist rigs, and an Invulnerability Field II as well (replacing one of the LSEs). The lowest resist on the first Vaga will be 48% (but it will have a very large buffer). The lowest resist on the second Vaga will be 73% (with about 60% of the buffer of the first). Quite a difference!
Finally, this rule applies to mission ships as well, particularly L4 mission ships, using self-reps. You only need enough buffer, whether shield or armor, that you feel comfortable with your ability to keep yourself repaired. All your other mid- or low slots, depending, should either go to additional resists, additional DPS, or additional utility e-war. The first will mean you take less damage, so you have to cycle your repper less often. The second and third will mean you kill the rats faster, with the same net result. Watch how your ship does during a mission to judge this. If you never dip below 50% armor or shields, depending, you should consider making some changes.
To summarize, it's just a good rule of thumb to keep in mind: if you have a decent Logis or self-rep, fit for resists. If you don't, fit for buffer.
(1) In Rote, if there are no ship losses, the Logis get to split the loot. As a result, Rote almost never has problems getting Logi pilots to X up. Other alliances that are having this problem, take note.
(2) A lot of factors play into this, including whether the reppers are meta or T2, whether I'm receiving boosts, whether those boosts are coming off a dedicated Fleet Command Ship, whether that Command Ship has a pilot with a Siege Mindlink implant, et cetera. Soon, another factor will come into play: whether the ganglinks on that boost ship are T1 or T2.