Rather than think of disadvantages, try to focus on outcomes. If a material is offered “too early”, first of all, what do you mean by “too early”? If you mean before the age listed in your album, try to focus differently. If you mean the results of the presentation are that the child is unable to engage with the material due to lack of sufficient preparation, then there really is no harm done. The child will simply not repeat the process, put the material away and choose something else that might hold more interest.  

There are very few materials in a Montessori environment that are based on sequence, namely language and math materials. Other materials and experiences are based on interest, movement abilities, and self-regulation. For example, if a child can walk and carry heavy objects (since approximately 18 months), that child can do something positive with almost any practical life activity. If the adults expect perfection the first time a child handles a particular piece of material, then the child will be presented with things much too late.  So, particularly in practical life, a child can do something positive with almost any activity.

For sensorial materials, interest is the primary driving factor.

In Montessori environments for older children, interest is also a driving factor but there are definitely some areas of the curriculum that are sequential and build on previous experiences.