A disclaimer added to a design registration makes it clear what parts of the whole design you have no wish to protect.
A limitation makes it clear what specific part of the design you wish to protect.
A good example of a disclaimer is when you file a design which includes a colour but as the design relates to the shape of the product then you should disclaim the colour ie “no claim is made to the colour shown in the illustration”
If you do not add this disclaimer, the protection given may be limited to the design in pink only.
Where you submit an image however you only wish to protect a part of the product that is featured in the image ie you submit a picture of a table but you only wish to protect the legs of the table featured in the image you should consider a limitation to the design of the legs and highlight the relevant part of the image by using a clear visual border or by greying out irrelevant parts of the design.
A disclaimer or limitation is imperative to ensure that you are protecting the right part of the design and that you don’t limit the scope of protection to colours and particular patterns.