War games are typically very expensive and time-consuming. The models cost a lot to acquire, take time to assemble, and then take more time to paint. The games themselves can last many hours. It is a hobby that requires a lot of investment.
Kill Team from Games Workshop is one of many smaller squad-level skirmish games. The advantages are many. For the full Warhammer 40,000 game, one needs are a bare minimum the core rulebook and a faction rulebook called a Codex for whatever army is being played. Many players like to run alliance armies that require multiple codexes and supplements. And then there is the cost for all the models. In contrast, Kill Team has all the basics in just one core book. Instead of buying the starter set, one could just buy the book and a single box of infantry to be ready to play the game. A few armies require more, but the majority are playable with just one squad box.
As a case in point, I am currently assembling an Eldar Harlequins Troupe. This army only has the one unit in its options list, but there are many ways to equip them with different weapons for different effects.
Image credit —Mine will be painted differently, and not as well, and not necessarily soon.
I crunched the numbers on how I could equip the six players in this theatrical troupe/spec-ops squad, and I can hit the 100 point target by choosing a pair of each different pistol option and a pair of each melee weapon upgrade. If I wanted to run a bare-bones squad equipped with only the standard wargear, I could fit another 2 troops for more bodies, but I think the game benefits more from the abilities gained through the special equipment. This squad needs to hit fast and hit hard to eliminate targets systematically, not try to match the opponent man-for-man or elf-for-ork.
Another obvious example is the Tau Fire Warriors squad that I had left over from the 7th Edition release of Kill Team. Ten soldiers plus a drone or two and a turret may require omitting someone from the squad to stay under 100 points.
The same applies to a Space Marine Tactical Squad, the Genestealer Cult, the Adeptus Mechanicus Vanguard/Rangers kit, and most of the other factions. Orks would need to be bolstered by a troop of Boyz backed up by Lootas, Burnas, and/or Gretchin, and the Imperial Guard Astra Militarum infantry squad would require two boxes, but they are the exceptions as far as I can tell.
Is it cheap? No. But it's not outrageous to dip your toe in and try a full-fledged game with minimal financial outlay and modest hobby time investment.