Tiagra and Sora are solid, reliable groupsets that work well for riders just getting into road cycling. Tiagra gives you 10 speeds and Sora gives you 9, compared to 12 speeds on Shimano 105. The shifting is still crisp and dependable—you just get fewer gear options and a bit more weight than higher-tier groupsets.
For commuting, casual fitness rides, or your first season on a road bike, Tiagra or Sora is honestly fine. You won't be held back from enjoying the sport. The real trade-off is upgrade potential: if you catch the cycling bug and want to upgrade components later, you'll likely need to replace the whole groupset rather than swap individual parts, since Tiagra/Sora use different compatibility standards than 105 and above.
If you can afford 105 without straining, it's the better long-term value. But if choosing 105 means buying a cheaper frame or skipping the bike altogether, start with Tiagra and put the savings toward actually riding.