I'll make fleets sometimes if I'm playing Advent and want to keep the ships near Guardians.  Otherwise I don't like making fleets.  I think the ships move in funny ways and I absolutely do not want a capital ship to be part of a fleet.

I dont use fleets either.  I would if it were not for the redicuous autojoin feature.  Ships that come out of the shipyard start with this turned on, and often join the wrong fleet.  If you have one massive fleet, its not an issue, but if you want a carrier group and a close combat group... newly built carriers will deside that the close combat group needs more carriers...

I will typically use Fleets now-a-days only for close in flak support of either a capital or other succeptable targets. I used to use fleets exclusively when I first started but ships on the outer periphery of the fleet range would often break off attack and try to reorganize themselves in the fleet and would be destroyed. I quit using them not long after I started playing.

I really wish they worked right. the auto-join, as mentioned, is annoying and makes you constantly fight to keep it in order.

The other day, though, I went looking for the formation button. I was sure there used to be one! oh! Its only for fleets? *sigh*

yeah, I'd like to use it to keep my guardians a certain distance from each other, and I'd probably do something similar with flak. Theres a bunch of other little things I would use it for, but to put it honestly: ignoring the fleets option just eliminates alot of annoyances