5 man 
HI links are the extreme example. Not all sectorials have the option to even do it and only a few are able to do it viably. It's a tremendous points and typically 
swc investment leaving little else to go around. 
 
 A fair portion of infinity gamers do play what they play for thematic reasons. Them aside, the most common links are 
LI ones. Generally, whether sectorial or vanilla, armies contain some number of 'cheer leader' type models. Putting them in a link team is an easy way to defend and make use of these models you may otherwise not actively or reactively use in your games, for the drawback of limited unit options. 
 
 For myself I don't see any unbalanced advantage a player using a link team has over one who's not, and vis versa. I'm not talking about the specific advantages and disadvantages of a link team, but the overall benefit to an army it brings with all other things considered. I've played extensively with and without link teams and really all that boils down to it when making an army list, is whatever floats my boat at the time. Including a link team or not doesn't have any effect on the perceived grosse 'competitiveness' of an army for me.
 
 A typical reason newer players (I had it as well) have issues with link teams is that it gives a very straightforward advantage to you F2F matchups, and reduces the effect of poor deployment and model placement with SSLvL2. Once you've played around a bit and found that you don't need to rely on SSLvl2 and can gain F2F advantages through other means, the benefits of link teams don't appear so substantial. And at the same time the drawbacks of them (primarily grouping and link leader shenanigans) seem bigger and overall the two balance out.
 
 Now, I pretty much just run links when I feel like taking the cats out for a spin. I usually play corregidor, but don't always use link teams in it, and rarely make use of increased 
AVA either. What's nice are mercenaries (for some 

). Although I should add that playing nomads can easily skew ones perceptions a bit. We've kinda got options to cover nearly all avenues so its far easier to patch holes when other armies really can't. Silly 
OP nomads