In the context of applied maths, physics and engineering. Videos/animations beat pictures and thousands of words, as is known to all. Is it bad to put too many videos/animations in a presentation? It's hard to define 'too' though.
If you have "too many", then, of course, it's "bad". This is more or less the definition of "too many".
How many is too many, is dependent on the situation and who you give a talk to. I have seen good presentations with videos illustrating a point and also short animations/memes which made the audience laugh and gave them time to breath after a long and heavy theoretical slides. (I don't like memes, but nevertheless I enjoyed those animations).
(Keep in mind that here are many mathematicians and a typical math talk has no animation/video, so you will probably get a lot of answers/comments similar to "I've never seen a good talk with animations in my life". It would be best if you would write your field.
The number of videos does not matter. What matters is:
- Is the video relevant?
- Is the video effective?
A video that clearly communicates the message of your talk should definitely be included. If it is off-topic, confusing, or has distracting flaws, it should be removed.
Do not be one of the many speakers who brings a video that does not work.
Do not use the "animations" built in to presentation software. They are distracting.
I disagree with @Hatschu. Do not use memes unless they are the topic of your presentation. Using memes suggests that your topic, and your spectator's time, are not important to you.
It is good to use things in moderation. If the videos or animations are really important to make your points use them but not in excess. If they are not meant to make your points, they will only serve as distractions to your audience. Also, consider the time you will have for the presentation and tailor things accordingly.