I really wish yamcha and tien got more action in dbz, despite the yamcha jokes he was a bamf in dragon ball.
Yamcha was only badass for a few episodes, as he was the first person we saw who could somewhat match Goku. Then he got scared away by Bulma cause girls frighten him. After the Pilaf saga, his only job was to get his ass kicked in the first round of the WMAT.
Tien did get quite a bit of action in DB, considering he was only introduced right before the final saga of DB. He beat Goku in the WMAT, was one of the few to stand a chance against Demon Piccolo, possibly beating him if not for the other demon taking the Mufuba Wave or w/e it's called, beat the crap out of Cyborg Tao, and he forced Goku to take off his training weights much early then either Kami or Goku expected him to.
Yamcha wasn't a very important person at all. He never was a real strong fighter, same goes for krillin.
But Tien and especially Piccolo should have had a bigger role later in the series. Tien was a very disciplined fighter and trained really hard throughout the series. But because he was human and the DBZ-makers didnt think that humans should be able to compete with saiyans no matter how hard they train, he never played a role in the whole series. Would have been cool if he was kinda the "monkstyle" fighter of the group. Maybe not the one who beats the big villian, but a helping hand killing some minions and rescuing the others from time to time. Okay he has his 2 appearances in cell and buu saga, but that was very very short.
And Piccolo... i mean, he is basically the fusion of earths "god" and "devil", therefore the ultimate protector of Earth. Before the Fusion he was able to compete with the two strongest non-SSJ Saiyans (Goku and Vegeta) and after the Fusion he the most powerful Z-Fighter for a short time. If the TBC makers wanted to he would have surely been able to stay on the level of the Saiyans.