One of the many things I’ve never figured out is why so many musicians, probably most, react in horror when you suggest that someone else sit in at a gig.
Seriously, it’s like you’re suggesting that they expose themselves to a contagious disease or radiation.
For example, just a typical blues or country gig at a bar. What are we talking about — a $50-or-$75-a-night gig?
Who gives a shit?
If you’re so shitty they’ll displace you, so what? You deserve it.
But let’s look at the positive things about inviting other people to sit in.
The first is that they’re simply there. Part of your probably sparse audience. The second is that they’ll bring along boyfriends/girlfriends and other friends. In a word, Audience.
And they’ll let other people know about it. Who will also be there.
And — gasp! — the player you’ll invite might add something wonderful musically, or maybe invite another musician who’ll add that.
Moral: Be kind, be generous. It´ll probably — no guarantees — pay off. The converse is even more true — be a constricted jerk and, guarantees here, it won’t pay off.
Be nice. Be generous. Invite your (competent) friends to sit in. You won’t regret it.