Most of the time you may want to use them defensely, esp. when you're kinda overhelmed with war and the enemy is too strong for your fleets to survive a direct attack.
Find out where he/they are going to attack, built bases there. Wait for him. You may want to have enough miniaturization and also planetary production to get a single tiny constructor out each turn. Once a certain amount ship-support is reached, alternate to produce cheap 1att 1def tiny fighter, although if the mps are enough could be any ship, just that it is important to get at least one ship per turn.
This will boost your military might far better than producing strong warships and will help you diplomatically.
Sometimes fleets packed full of tiny fighters are a means to victory, esp. against single very strong hardhitting ships like the dreadlords, as they can only destroy one ship per round. This will prolong the fight and the rest of your ships will do lots of damage. (ignore defenses in this scenario entirely)
Another point is that this way of doing war is pretty econnomically. The big downside is that starbases cannot move or attack by themselves (would be really fun if they could) as well as solo starbases are rather weak and oftentimes targeted by the AI.
If you're playing with Yor or a custom race that has their superability the -2 shipsspeed module and the ones giving you additional speed are absolutely fantastic. You can slow enemy fleets to 1 speed and outmanoveur them easily even without having engines on your ships.
I remember one game on suicidal I had to do this and turn the game basically into a stalemete because the Altarians had completely outresearched everybody and were unbeatable until I caught up. As I had only some basic research into weapons/hulls/speed (which you can leave out, esp. weapons take pretty long, this will negate completely your techcost of starbase/minia/fleets) I took this also to an offensive approach.
Invading their systems with fleets of constructors and tiny fighters, getting my military starbases up there, then destroying the defenders, invading planets. (the starbases from that point on serve defensively as new worlds usually can't stand an invasion). Only concern is that you're getting intercepted so you definitely need some engines and sensor ships.
What you also can do it to pair your tiny fighter fleets with a flagship that is build around absorbing the enemies attack. The intention is to protect your tiny ships and cash in on the fire power they get from the starbases, if you do it correctly the flagship should always survive and overtime become pretty strong.