Advantages of Blockboard
Lighter in weight:
The blockboard core is made from solid blocks of wood that is usually obtained from softwood trees such as pine, mango or cedar. In comparison good quality plywood is often made from veneers obtained from hardwood trees (e.g. Gurjan wood which is very popular in India), and the high quality solid wood that is used in furniture is generally obtained from hardwood trees such as teak wood.
Because hardwood is denser than softwood, its weight is also more. So if you take a piece of plywood or solid wood and compare its weight with a blockboard piece of the same size, you will find that blockboard is lighter in weight.
The advantage of being light-weight is that it can be more easily transported to the end-location. The most common application of this is in the case of doors that we use inside our homes. Doors are very often made from blockboard.
Lesser tendency to sag or bend
In cases where very long pieces of wood are required in furniture making, such as in long book shelves, panels, benches and tables, blockboard is often preferred over plywood. This is because long plywood pieces tend to bend in the middle, whereas blockboard is stiffer and less prone to bending. When the board length exceeds 6 or 7 feet, blockboard is generally used instead of plywood.
Another important advantage of blockboard is that it is cheaper than good quality solid wood as well as hardwood plywood. This is because softwood costs lesser than hardwood.
Better than Particle Board and even MDF
Compared to other engineered wood products that are popular these days, such as Particle boards(which is made from small particles of wood flakes/chips) and even MDF (which is made from wood fibers), blockboard is considered to be better. It is comparatively stronger and lasts longer. Also from the carpenters' point of view, the added advantage of blockboards is that it is easier to work with, since it can take nails as well as screws. In comparison, particle board and MDF do not have much nail holding strength and hence only screws are used on them. In fact most of the carpenters in India who make custom-built furniture work only with plywood and blockboards, and not MDF or Particle boards.
Disadvantages of Blockboard
Not as strong as plywood or good quality solid wood
The major disadvantage of blockboards is that since softwood is used in its making, it is not as strong as quality solid wood (such as teak wood) or hardwood plywood. So when it comes to furniture making, plywood is the preferred choice of material (except for cases where lengthy wood pieces have to be used). However, if instead of softwood blocks, hardwood is used to form the blockboard core (some manufacturers do this), then the strength of the blockboard increases.
Minor disadvantage for carpenters
In some cases, the blocks (also called strips or battens) that form the core, may have small gaps between them. These gaps cannot be seen from outside since there is layer of veneer on top. Because of this, sometimes the nails that are driven through the board surface may not go into the wood but rather in the gaps between the blocks, which can adversely affect the holding strength of that nail. But this is only a minor drawback, that occurs only sometimes.