Signature images go wrong in two predictable ways: too large in bytes, or too large on screen. Both are easy to avoid.
A signature image is attached to every email you send, and to every reply in a long thread. A one megabyte logo becomes twenty megabytes across a busy day, which is why some organisations set limits on them.
Many email clients block images by default, so your signature may simply not appear. That is a good reason to keep your name and contact details as real text and let the image be decoration rather than the only place the information lives.
Check it on a phone. A logo that looks modest on a wide desktop signature can dominate the screen on mobile, where most email is now read.
Around 300 pixels wide for a logo and under 50 kilobytes. Smaller is better.
Many clients block remote images by default. Keep essential details as text.
No.