You should preface this with some important information about what that does.

There are some trade-offs!

Changing that setting to 1 gives you weaker anonymity guarantees. Using multiple guards spreads your traffic across different IP addresses, making it harder for an adversary who controls a subset of the network to correlate your activity.

Reducing to a single guard concentrates all traffic through one point, increasing the chance that a hostile relay could observe a larger fraction of your streams...