TP is sacrificing lane/kill pressure in an attempt to farm safely and use your TP either to continue to farm (backing at normally bad moments but making up for it via teleport) to make plays around the map to snowball a lead for your team and thus win the game. It's a common thing to do when you're not going to win lane due to an unfavourable matchup or you simply wish to roam. People often forget that Teleport (while there is a long duration to actually teleport) is great deterrent and always a threat. If you don't take into account someone's TP is up and they're paying attention, you are fucked. There's also the fact that it's safe if your smart where you use it and where you teleport to exactly. You won't get caught out teleporting at your tower after pushing the wave, for example.
Teleport is the second strongest summoner spell, second only to Flash (note that Flash is a summoner spell that is considered mandatory and can literally turn games around) and so unless it gets nerfed to literal unplayable tier (think a 600 second cooldown, a longer cast time, some completely stupid drawback or any combination of the three) it's always going to be relevant.
On the other hand, if a support takes Teleport, ask them if they messed up their Summoner Spells. That doesn't make sense.