neowin[.]net/news/microsofts-default-bitlocker-on-your-windows-11-pc-is-hitting-even-the-fastest-ssds-hard/
tomshardware[.]com/news/windows-software-bitlocker-slows-performance
BitLocker encrypts the entire drive, so if your laptop is stolen for example, the thief would not be able to access anything stored on the drive, unless they brute forced the password etc. IOW if you use password for the password that's not going to be much protection at all. Since Windows has to decrypt every file before opening it, then encrypt every file that's going to be saved or written to disk, you'd logically expect there would be a performance hit. The same would be true of the open source VeraCrypt. Tom's Hardware took a look to see just how big of a hit you might expect, though for their tests they used a VERY fast drive. While they measured what would seem to be a significant loss of performance, because the drive itself is so fast you'd probably never notice -- you would however probably feel / see the difference using a slower drive.
Note that Microsoft is pushing BitLocker with Win11, so new installations & PCs/laptops may come with BitLocker already enabled.