In the ’80s, nearly every guitar player drenched their sound in copious amounts of chorus and/or octave effects. It created many of the most distinctive songs and tones of the (think “In A Big Country” by Big Country and pretty much anything by The Cure from that era). Tastes change, and we don’t hear quite as much chorus as we did back then — but it’s still a vital, essential and much-used effect!
But chorus, octave and other modulation effects are useful for more than just guitar; the key is to use the effect carefully to thicken up a bass sound. The trick to subtle chorus and octave effects that add thickness and depth to an otherwise dry bass guitar is to keep the signal mostly dry, either using the blend control on the chorus effect or by running the chorus in parallel with the dry signal.
Be sure to keep the depth and wet amount below 30% or so, so that your signal is mostly dry. Add just enough modulation to enhance depth and thickness without the effect taking over. The exact amount you’ll want to dial in depends on the type of music and venues you’re playing.
Another trick is to use a crossover to split the bass signal before the chorus, then feed the lows straight through to the amp while the highs get a bit of chorus. This maintains solid bottom end, while thickening the highs and mids.