DO NOT consider this legal advice. I am not an attorney. This is simply what I learned in film school, in one of the most boring and arduous classes I had to take: The Law and Photography.
A Non-Exclusive vs Exclusive Digital Rights License has to do with ownership and use of the material created. Most don't understand that when they engage a Photographer, they do not own the images created for them. The Photographer owns the images as the creator and retains ownership rights to the images protected by Copyright Law. The Photographer issues a Rights License to the Client so they can use the images. These licenses are Digital or Print, in the case of physical media.
Exclusive - The Client is the only one who can use the images. Nobody else can, including the Photographer who created the images. (Unusual)
Non-Exclusive - The Client is allowed to use the images and the Photographer also retains the right to use the images as well. (Portfolio, exhibitions, galleries, online, whatever) (Normal)
You can issue a combination of these as well, for example, giving the Client Exclusive Rights for 6 months and after that, it becomes Non-Exclusive.
NOTE: If a "Work For Hire" situation is created, then the work would be owned by the hiring party and not the Photographer, who has become an employee. This would happen by a company or individual hiring you, putting you on the payroll, issuing paychecks, withholding taxes...all the trappings of a job and working for someone else. This would be unusual and all parties would well understand the situation and ownership of the work created.
So, why do this? Well, if I was to issue an Exclusive Rights License, or allowed a "For Hire" situation to exist, then I cannot do anything with any images or work I create. It's all dead to me and the time and energy I've put into it is wasted. I can't use it for anything else. I can't show it off in my Portfolio, exhibit at a gallery, sell to another party (Stock B-Roll)....anything. IF I were to ever allow this to happen, I would make sure that the $$$$ I'm being paid would fairly reflect the loss of possible future income and promotional consideration. In other words, if you want to "own" the work or have Exclusive Rights to the work, it's gonna cost 10X what you'll pay for Non-Exclusive Rights. So, I issue licenses for the work I create on every job.
Obviously, there is a WHOLE LOT MORE to this subject and above is a very brief overview. There is so much more minutiae, details, exceptions, qualifiers, you name it...I could not possibly cover it in an Internet Post. Please seek legal advice in your area from an attorney and/or do your own research into this. There are plenty of great books on this including the textbook I had to study in film school. (Torture, plain and simple torture)
Filters - Maybe, but I really don't like them and won't use one rather than seek better conditions. Polarizers are great for glare off reflective surfaces and can help, but you can tell when they're being used. Unless its the only opportunity you'll have to get the shot, to me it's just lack of professional commitment to quality and an effort to produce a truly great work. Plan the shot and get it when the conditions are right. If not, try again and don't settle for excuses. Goes along with "Get it right in camera" and don't depend on "Posting" it out.
Just IMHO, so filter users don't flame me. You do you and own it.