If you are job hunting, you should send your resume to recruiters.
Different recruiters know about different positions. They do not usually know about the same ones. This is particularly true with retained firms. By sending your resume out widely, you will be placed in many different confidential databases and be alerted of many different positions. If you send your resume to only a few, it may be that none you send to will be working with positions which are suited for you. Throw your net widely. If you change jobs, it is also wise to send follow-up letters to the recruiters and alert them of your new career move. Many search firms follow people throughout their careers and enjoy being kept up-to-date. It is a good idea to have your resume formatted in plain text so you can copy and paste it into email messages when requested to do so. Then, follow up with a nicely formatted copy on paper by postal mail.
Some people estimate that only 1% to 3% of all resumes sent will result in actual job interviews. So, if you only send 50 resumes, you may only have less than 2 interviews, if that many. Send your resume to as many recruiters as you can. It is worth the postage. Generally, recruiters will not share your resume with any employer or give your name to anyone else without obtaining your specific permission to do so. The recruiter will call first, talk to you about a particular position and then ask your permission to share your resume with that employer.