The Flash’s Time Wraiths spoiled the series. Barry Allen has been able to time travel since mid-season 1. As a speedster, this ability typically comes with the territory and, if Barry runs fast enough, he can go back to the past or future whenever he pleases. Of course, Barry’s time-traveling escapades have been called into question considering how damaging it can be to the timeline’s natural events. Any change, no matter how major or minor, can alter life events and characters’ histories. The Time Wraiths, who are ghastly, monster-like creatures, are the keepers of the timeline and have come after speedsters for manipulating it to any extent. However, they’ve largely been a hindrance to Barry’s growth as a speedster.
Barry has changed the timeline enough to frustrate those closest to him. While he’s been told that traveling to the past will have major repercussions, he's continued to do so regardless of these warnings. In The Flash season 3, Barry was given a much-needed lecture by Jay Garrick, the Flash of Earth-3. In short, the scarlet speedster couldn't go back in time to change something whenever he wanted to or risk causing irreparable cracks in the timeline. For a while, it seemed he had learned the lessons of what tampering with the timeline could do.
However, the introduction of the Time Wraiths actually worked against Barry's personal growth because it became (at least in part) about assuaging and avoiding these creatures rather than about Barry himself. Knowing that the Time Wraiths are there to hunt and not teach turns them into external and terrifying adversaries that Barry attempts not to anger. As such, several of Barry's time trips became less about understanding that tampering with the past has severe repercussions and more about ensuring that he isn't caught.
The consequences of time travel was never an issue that Barry fully contended with. Sure, he faced admonishment for his actions at different (and inconsistent) points throughout the series’ six seasons. But, the speedster’s personal journey as a time traveler never amounted to any self-discovery on Barry’s part. Nor was there any character development or explanation for how he used it to overcome past trauma that he never actually faced or let go. The Time Wraiths transformed into yet another obstacle to overcome, leaving a lot to be desired with regards to character growth and depth. Without them, the series would have greatly benefitted and Barry would have been able to tackle his time travel pursuits in a more personal manner.
What’s more, the Time Wraiths are inconsistent villains who only seem to appear at random. Considering all of the times that Barry has time-traveled and gotten away with it, the Time Wraiths have only ever come after him a few times. The first occurrence was in late season 2, when Barry briefly impersonated a past version of himself to obtain information on Eobard Thawne. Barry’s final encounter with the Time Wraiths happened while within the speed force with daughter Nora West-Allen (Jessica Parker Kennedy) in The Flash season 5. The wraiths didn’t appear at all when Barry went back in time to save his mom and created Flashpoint, an alternate timeline. They haven’t appeared in other major instances, either, and their presence has been nothing more than a plot contrivance.