There are good reasons to enter some competition events during a base phase. But, that doesn't mean that each event should be treated with an "A-race" type approach.
When entering a competition event during base phase, athletes may choose to view a competition event with a "major race" type objectives - which usually means focusing on a result, a time, or on not getting beaten by a particular competitor - and/or ensuring that you are sufficiently rested/recovered leading up to the event. Approaching every competition event in this way (that is, emphasising a results based objective in a base training phase) applies a shorter term focus and can create an expectation/pressure that the athlete needs to be at their best/peak for that event.
We shouldn't be aiming for peak performance in base phase.
Treating every race as a "major race" - whether in base phase, or another phase - conflicts with training objectives geared for longer term performance improvement and may inhibit peaking at a time (i.e. "an A-race") when peak performance is actually desired. In other words, it may present a barrier to achieving a higher level of performance at a "special" event.
It can flatten the peak.
Result focused "racing" in a base period can create tension between short term and longer term objectives - it may shift a mindset from a training mindset, which is one that requires a particular focus and accepts/acknowledges that we are going to be fatigued and not out best during this phase, to one which requires, and possibly demands, that we need to be rested/recovered and performing at a race-type standard.
Resting may mean adapting or forgoing training sessions intended to incrementally progress some aspect of performance geared towards a more substantial race objective. In addition to that, depending on macro-cycle timing, there may also be additional recovery considerations following a race event - that may mean that the event has a residual impact on training.
When selecting competition events in a base phase, consider setting an objective that is not result based, and pick the timing of those events carefully to integrate them into your preparation in a way which complements/reinforces your other training requirements. For example, consider rehearsing a pacing strategy, a nutrition strategy or trialing equipment - in a race environment - that allows you to gather information that you can exploit in your major event.
Pick your battles. Think longer term.
Seeya out there,
Steve